1. Field of the Invention
The present invention relates to spin valve thin film magnetic elements and thin film magnetic heads. In particular, the present invention relates to spin valve thin film magnetic elements in which shunt losses of sensing currents are reduced and rates of change in magnetoresistance are increased.
2. Description of the Related Art
Among magnetoresistive effect type magnetic heads, there are MR (Magnetoresistive) heads, providing an element showing a magnetoresistive effect, and GMR (Giant Magnetoresistive) heads, providing an element showing a giant magnetoresistive effect. In the MR head, the element showing a magnetoresistive effect is made to have a single-layer structure made of magnetic materials. On the other hand, in the GMR head, the element showing a magnetoresistive effect is made to have a multi-layer structure composed of laminated plural materials. There are several kinds of structures generating giant magnetoresistive effects, and the spin valve thin film magnetic element is the one having a relatively simple structure, and having a high rate of change in resistance to an external magnetic field.
Recently, requirements for further increase in the magnetic recording density have been even more intensified, and the spin valve thin film magnetic elements, which have the potential to fulfill further demands for increases in magnetic recording density, have attracted great amounts of attention.
Next, a conventional spin valve thin film magnetic element is explained referring to the drawings. FIG. 15 is a schematic sectional view of a conventional spin valve thin film magnetic element 101 viewed from a magnetic recording medium side. FIG. 16 is a schematic sectional view of the spin valve thin film magnetic element 101 viewed from a track width direction.
On the top and bottom of the spin valve thin film magnetic element 101, shield layers are formed via gap layers, and a reproducing thin film magnetic head is composed of the spin valve thin film magnetic element 101, gap layers, and shield layers. A recording inductive head may be laminated on said thin film magnetic head.
The thin film magnetic head is provided on an end portion of a trailing side of a floating slider, etc., together with an inductive head, to constitute a thin film magnetic head, and to detect recording magnetic fields of magnetic recording media such as hard disks.
In FIGS. 15 and 16, the Z direction shown in the drawings is a moving direction of the magnetic recording medium, the Y direction shown in the drawings is a direction of a leakage magnetic field from the magnetic recording medium, and the X1 direction shown in the drawings is a direction of the track width of the spin valve thin film magnetic element 101.
The spin valve thin film magnetic element 101, shown in FIG. 15 and FIG. 16, is a bottom type single spin valve thin film magnetic element constituted by orderly laminating an antiferromagnetic layer 103, a pinned magnetic layer 104, a nonmagnetic conductive layer 105, and a free magnetic layer 111.
In FIG. 15 and FIG. 16, the numeral 100 shows an insulating layer formed from Al2O3, etc., and the numeral 102 shows a substrate layer made of Ta, etc., laminated on the insulating layer 100. The antiferromagnetic layer 103, the pinned magnetic layer 104, the nonmagnetic conductive layer 105 formed from Cu, etc., and the free magnetic layer 111 are laminated in order on the substrate layer 102, and a cap layer 120 formed from Ta, etc., is laminated on the free magnetic layer 111.
Thus, each layer from the substrate layer 102 to the cap layer 120 is laminated in order to constitute a laminate 121 having a width meeting the track width, and having a sectional view of nearly trapezoidal shape.
The pinned magnetic layer 104 formed from, for example, Co, is laminated in contact with the antiferromagnetic layer 103, and an exchange coupling magnetic field (an exchange anisotropic magnetic field) is generated on the boundary of the antiferromagnetic layer 103 and the pinned magnetic layer 104; then, the direction of magnetization of the pinned magnetic layer 104 is pinned in the Y direction shown in the drawings.
The free magnetic layer 111 is composed of a nonmagnetic intermediate layer 109, and the first free magnetic layer 110 and the second free magnetic layer 108 holding said nonmagnetic intermediate layer between these. The first free magnetic layer 110 is provided on the cap layer 120 side of the nonmagnetic intermediate layer 109, and the second free magnetic layer 108 is provided on the nonmagnetic conductive layer 105 side of the nonmagnetic intermediate layer 109. The thickness t1 of the first free magnetic layer 110 is slightly greater than the thickness t2 of the second free magnetic layer 108.
The first free magnetic layer 110 is formed from a ferromagnetic material such as a NiFe alloy, and the nonmagnetic intermediate layer 109 is formed from a nonmagnetic material such as Ru.
The second free magnetic layer 108 is composed of a diffusion preventing layer 106 and a ferromagnetic layer 107. The diffusion preventing layer 106 and the ferromagnetic layer 107 are both made of ferromagnetic materials, the diffusion preventing layer 106 is formed from, for example, Co, and the ferromagnetic layer 107 is formed from the NiFe alloy. The first free magnetic layer 110 and the ferromagnetic layer 107 are preferably composed of the same material.
The diffusion preventing layer 106 is provided to prevent the mutual diffusion of the ferromagnetic layer 107 and the nonmagnetic conductive layer 105, and to increase the GMR effect (xcex94MR) generated at the interface of the nonmagnetic conductive layer 105.
When saturation magnetizations of the first free magnetic layer 110 and the second free magnetic layer 108 are shown by M1 and M2, respectively, the magnetic film thickness of the first free magnetic layer 110 and the second free magnetic layer 108 become M1xc2x7t1 and M2xc2x7t2, respectively.
Then, the free magnetic layer 111 is constituted so that the magnetic film thickness of the first free magnetic layer 110 and the magnetic film thickness of the second free magnetic layer 108 are made to meet the relation M1xc2x7t1 greater than M2xc2x7t2.
The first free magnetic layer 110 and the second free magnetic layer 108 are antiferromagnetically coupled to each other. That is, when the direction of magnetization of the first free magnetic layer 110 is oriented in the X1 direction shown in the drawings by bias layers 132 and 132, the direction of magnetization of the second free magnetic layer 108 is oriented in the direction opposite to the X1 direction.
The relationship of the magnetic film thickness of the first free magnetic layer 110 and the magnetic film thickness of the second free magnetic layer 108 is specified as being M1xc2x7t1 greater than M2xc2x7t2, to create a state in which the magnetization of the first free magnetic layer 110 remains, and to orient the direction of magnetization of the free magnetic layer 111, as a whole, in the X1 direction shown in the drawings. At this time, a magnetic effective film thickness of the free magnetic layer 111 becomes (M1xc2x7t1xe2x88x92M2xc2x7t2).
Thus, because the first free magnetic layer 110 and the second free magnetic layer 108 are antiferromagnetically coupled to make each direction of magnetization antiparallel, and the relation of each magnetic film thickness is specified as being M1xc2x7t1 greater than M2xc2x7t2, these are made to become the artificial ferrimagnetic state (synthetic ferrimagnetic state).
Therefore, the direction of magnetization of said free magnetic layer 111 and the direction of magnetization of said pinned magnetic layer 104 are cross each other.
The bias layers 132 and 132 are formed on both sides of the laminate 121. These bias layers 132 and 132 orient the direction of magnetization of the first free magnetic layer 110 in the X1 direction shown in the drawings, to make the free magnetic layer 111 a single domain, and to suppress the Barkhausen noise of the free magnetic layer 111.
The numerals 134 and 134 show conductive layers formed from Cu, etc. Said conductive layers 134 and 134 apply a sensing current (a detection current) to the laminate 121.
A bias substrate 131 made of, for example, Cr, is provided between the bias layer 132 and the insulating layer 100, and between the bias layer 132 and the laminate 121, and an intermediate layer 133 made of, for example, Ta or Cr, is provided between the bias layer 132 and the conductive layer 134.
In the spin valve thin film magnetic element 101, when the direction of magnetization of the free magnetic layer 111, oriented in the X1 direction shown in the drawings, is changed due to a leakage magnetic field from a recording medium such as a hard disk, the electrical resistance is changed in connection with the magnetization of the pinned magnetic layer 104, pinned in the Y direction shown in the drawings, and, then, the leakage magnetic field from the recording medium is detected based on the change in voltage due to the change in the electrical resistance value.
Because the free magnetic layer 111 is composed of the first and second free magnetic layers 110 and 108, being antiferromagnetically coupled to each other, the direction of magnetization of the free magnetic layer 111, as a whole, changes due to a small amount of external magnetic field to increase the sensitivity of the spin valve thin film magnetic element 101.
In particular, it becomes possible to decrease the effective film thickness (M1xc2x7t1xe2x88x92M2xc2x7t2) of the free magnetic layer 111 by properly adjusting the film thickness, etc., of the first and second free magnetic layers 110 and 108, and, therefore, the direction of magnetization of the free magnetic layer changes easily due to a small amount of external magnetic field to increase the sensitivity of the spin valve thin film magnetic element 101.
In the conventional spin valve thin film magnetic element 101, there have been problems in that because the free magnetic layer 111 has a lamination structure of three layers composed of the first and second free magnetic layers 110 and 108, and the nonmagnetic intermediate layer 109, the laminate 121 itself is made thick, the shunt loss occurs due to a reduction of conduction of electrons flowing through the nonmagnetic intermediate layer 105 by the generation of a shunt of the sensing current, and the rate of change in magnetoresistance of the spin valve thin film magnetic element is reduced.
The present invention is was made taking the aforementioned circumstances into consideration. It is an object of the present invention to provide spin valve thin film magnetic elements in which the detection sensitivity of external magnetic fields is increased, the shunt loss of the sensing current is reduced, and the rate of change in magnetoresistance is increased. It is another object of the present invention to provide thin film magnetic heads comprising the spin valve thin film magnetic elements.
To achieve the aforementioned objects, the following constitution is adopted in the present invention.
A spin valve thin film magnetic element of the present invention comprises an antiferromagnetic layer; a pinned magnetic layer formed in contact with said antiferromagnetic layer, in which the direction of the magnetization is pinned by an exchange coupling magnetic field with said antiferromagnetic layer; a nonmagnetic conductive layer in contact with said pinned magnetic layer; and a free magnetic layer in contact with said nonmagnetic conductive layer, in which said free magnetic layer is composed of a nonmagnetic intermediate layer, and first and second free magnetic layers holding said nonmagnetic intermediate layer therebetween; said first free magnetic layer and said second free magnetic layer are antiferromagnetically coupled so as to be in a ferrimagnetic state; and a resistivity of said first free magnetic layer, in the far side from said nonmagnetic intermediate layer, is higher than a resistivity of said second free magnetic layer, in said nonmagnetic intermediate layer side.
According to said spin valve thin film magnetic element, because the resistivity of the first free magnetic layer, constituting the free magnetic layer, is higher than the resistivity of the second free magnetic layer, a detection current is difficult to flow through the first free magnetic layer, and, therefore, the shunt of the detection current is suppressed, the shunt loss is reduced, and the rate of change in magnetoresistance of the spin valve thin film magnetic element may be increased.
Research was performed, regarding the conventional spin valve thin film magnetic element 101 as a base constitution, to determine the degree of the effect which could be specifically anticipated when the shunt of the sensing current was suppressed.
In the conventional spin valve thin film magnetic element 101, when the first free magnetic layer is made of 3 nm NiFe alloy, the rate of change in magnetoresistance is 7.3%; however, when the first free magnetic layer and the nonmagnetic intermediate layer are removed from the constitution of the conventional spin valve thin film magnetic element, to reduce the shunt of the sensing current, the rate of change in magnetoresistance becomes 8.0%, which is an increase of about 10%. Thus, by suppressing the shunt of the sensing current, a large increase in the rate of change in magnetoresistance can be expected.
However, in the constitution wherein the first free magnetic layer and the nonmagnetic intermediate layer are removed from the constitution of the conventional spin valve thin film magnetic element, as the free magnetic layer does not enter the ferrimagnetic state, the detection sensitivity for the external magnetic field is remarkably reduced.
Therefore, according to the present invention, a novel particular effect can be obtained, wherein the rate of change in magnetoresistance can be increased, while maintaining the detection sensitivity for external magnetic fields.
The spin valve thin film magnetic element of the present invention may be the aforementioned spin valve thin film magnetic element, wherein the aforementioned first free magnetic layer is composed of the first ferromagnetic layer in contact with the aforementioned nonmagnetic intermediate layer, and the second ferromagnetic layer in contact with said first ferromagnetic layer; said first ferromagnetic layer is antiferromagnetically coupled to the aforementioned second free magnetic layer holding the said nonmagnetic intermediate layer therebetween; and a resistivity of said second ferromagnetic layer is higher than a resistivity of said first ferromagnetic layer.
According to such a spin valve thin film magnetic element, because the first ferromagnetic layer, constituting the first free magnetic layer, is antiferromagnetically coupled to the aforementioned second free magnetic layer, and the resistivity of the second ferromagnetic layer is higher than the resistivity of the first ferromagnetic layer, the first free magnetic layer itself can be antiferromagnetically coupled to the second free magnetic layer to enter the ferrimagnetic state, and the shunt loss of the detection current can be reduced by increasing the resistivity of the first free magnetic layer, as a whole.
The aforementioned first free magnetic layer is preferably made of either a NiFeX alloy, where X is one or more elements selected from the group consisting of Cr, V, Nb, Hf, Ta, Mo, and W, or a CoMT alloy, where M is one of Zr and Hf, or both, and T is one of Nb and Ta, or both.
The aforementioned first ferromagnetic layer may be made of a NiFe alloy, and the aforementioned second ferromagnetic layer may be made of either a NiFeX alloy, where X is one or more elements selected from the group consisting of Cr, V, Nb, Hf, Ta, Mo, and W, or a CoMT alloy, where M is one of Zr and Hf, or both, and T is one of Nb and Ta, or both.
The spin valve thin film magnetic element of the present invention is the aforementioned spin valve thin film magnetic element, wherein said thin film magnetic element may be constituted so that a part adjacent to the aforementioned nonmagnetic intermediate layer, of the aforementioned first free magnetic layer, is made of a NiFe alloy phase; and a part in the far side from said nonmagnetic intermediate layer is made of either a NiFeX alloy phase, where X is one or more elements selected from the group consisting of Cr, V, Nb, Hf, Ta, Mo, and W, or a CoMT alloy phase, where M is one of Zr and Hf, or both, and T is one of Nb and Ta, or both; and a composition of a part held between said NiFe alloy phase, and said NiFeX alloy phase or CoMT alloy phase, is gradually changed from the NiFe alloy phase to the NiFeX alloy phase or CoMT alloy phase, as the distance from said nonmagnetic intermediate layer is increased.
The spin valve thin film magnetic element of the present invention is the aforementioned spin valve thin film magnetic element, wherein the aforementioned NiFeX alloy is preferably represented by the formula NiaFebXc, where X is one or more elements selected from the group consisting of Cr, V, Nb, Hf, Ta, Mo, and W, and a, b, and c are compositions being within the ranges 60 atom %xe2x89xa6axe2x89xa690 atom %, 5 atom %xe2x89xa6bxe2x89xa630 atom %, and 0 atom % less than cxe2x89xa615 atom %.
The spin valve thin film magnetic element of the present invention is the aforementioned spin valve thin film magnetic element, wherein the aforementioned CoMT alloy is preferably made of a constitution comprising an amorphous phase as a primary phase, and is preferably represented by the formula COdMeTf, where M is one of Zr and Hf, or both, and T is one of Nb and Ta, or both, and d, e, and f are compositions being within the ranges 78 atom %xe2x89xa6dxe2x89xa692 atom %, e=g(100-d) atom %, f=(100-d-e) atom %, and said g is within the range 0.1xe2x89xa6gxe2x89xa60.5.
The spin valve thin film magnetic element of the present invention is the aforementioned spin valve thin film magnetic element, wherein the aforementioned thickness s of the first ferromagnetic layer is preferably within the range 0 nm less than sxe2x89xa61 nm.
When the thickness s of the first ferromagnetic layer is 0 nm, i.e., the first ferromagnetic layer, made of the NiFe alloy, is not provided, the second ferromagnetic layer, made of the NiFeX alloy or the CoMT alloy, comes into contact with the nonmagnetic intermediate layer, and this is not preferable because these alloys are inferior in magnetic properties compared to the NiFe alloy, these cannot be antiferromagnetically coupled easily to the second free magnetic layer, and cannot make the free magnetic layer enter the ferrimagnetic state.
When the thickness s of the first ferromagnetic layer is more than 1 nm, this is not preferable because the film thickness of the free magnetic layer itself is increased to easily generate the shunt of the detection current.
The aforementioned second free magnetic layer is preferably composed of a single-layer film made of one selected from the group consisting of Co, a CoFe alloy, a NiFe alloy, a CoNi alloy, and a CoNiFe alloy, or is preferably composed of a multi-layer film in which two or more kinds of said single-layer films are laminated.
The aforementioned antiferromagnetic layer is preferably made of either an alloy represented by the formula Xxe2x80x94Mn, where X is an element selected from the group consisting of Pt, Pd, Ru, Ir, Rh, and Os, or an alloy represented by the formula Xxe2x80x2xe2x80x94Ptxe2x80x94Mn, where Xxe2x80x2 is one or more elements selected from the group consisting of Pd, Cr, Ni, Ru, Ir, Rh, Os, Au, and Ag.
The aforementioned pinned magnetic layer is preferably composed of a nonmagnetic layer, and the first and the second pinned magnetic layers holding said nonmagnetic layer therebetween, the directions of magnetization of said first and second pinned magnetic layers are preferably made antiparallel, and said first and second pinned magnetic layers are preferably made to enter the ferrimagnetic state.
A thin film magnetic head of the present invention provides the aforementioned spin valve thin film magnetic element.